1. Field of the Invention
The invention relates to systems utilizing digital processors particularly with respect to data input/output apparatus therefor.
2. Description of the Prior Art
Systems are prevalent that include a digital processor for operating upon large amounts of analog, digital and discrete input data to provide large amounts of analog, digital and discrete output data for use in utilization devices. Such systems are finding wide spread usage in modern aircraft for integrating the various aircraft flight data sensors and electronic equipment such as radios and the like to provide the necessary control, display and annunciation functions to the flight controls, flight instruments, display panels and the like. The analog inputs to such systems normally include gyro synchro pickoffs, control wheel force or displacement sensors as well as autopilot control inputs such as pitch and bank wheels and the like. Such systems also include autopilot mode controllers with numerous push buttons utilized for mode selection, which push buttons may be individually and selectively illuminated by lamps included therein. A computer control panel with an alphanumeric data entry keyboard with illuminated key annunciations may also be included for entering data into the system. Such systems also include numerous displays such as segmented alphanumeric readout devices operated by digital signals normally in binary coded decimal format and additionally include a large variety of discrete inputs such as valid/invalid signals from various sensors and equipments, discrete switch positions and the like. Digital signals are also entered from digital data sources such as the system air data computer, etc.
Such prior art systems also provide large amounts of analog, digital and discrete output data such as the analog outputs to the various control surface servos, analog signals to the various flight instruments as well as digital data to the displays and discrete outputs such as instrument failure warning flags and the like.
In these prior art systems the analog signals are generally multiplexed into a single analog-to-digital converter whose sequential outputs are entered into the system digital processor in bit parallel fashion via a parallel bit data bus. The outputs of the alphanumeric data entry keyboards, the mode selection push button panels and the like are encoded into binary digital format and these binary data entered into the data bus in bit parallel fashion either prior to or subsequent to the entry of the analog data. Generally the discrete inputs are multiplexed or combined in latches for parallel entry into the data bus.
In a similar manner in the prior art systems the analog outputs are provided from the data bus as a sequence of bit parallel words that are sequentially strobed into a digital-to-analog converter whose output is multiplexed to the various analog utilization devices. The digital outputs such as the illumination of the keyboard lamps and the energization of the digital displays are sequentially provided in bit parallel fashion through decoding circuits associated with the various digital utilization devices. The discrete outputs are provided in parallel fashion and demultiplexed into the various discrete utilization devices.
It is thus appreciated that since the data enters and exits the system primarily in bit parallel form, numerous line drivers and receivers as well as logic circuits are required. Additionally, numerous encoders and decoders are necessitated for the keyboards and displays as well as complex multiplexers for the various digital and discrete data. Thus the prior art systems require large amounts of expensive input/output components, increasing the bulk, weight and power dissipation of the system which requirements are undesirable particularly in aircraft environments. These prior art arrangements necessitated large numbers of interface wires and connections thereby decreasing reliability and complicating installation procedures resulting in increases in installation errors.
It will be appreciated that because of the numerous encoders and decoders required for the input and utilization devices, significant amounts of buffering between different logic levels is required. It will furthermore be appreciated that because of the requirement for sequential input and output with respect to all of the analog, digital and discrete data, substantial computer time is required for the system I/O functions.
Because of the significant number of input and output lines required to perform the I/O function in prior art apparatus large numbers of line buffers are required in interfacing the various logic levels often utilized in such systems.
It will be appreciated that in the prior art systems discussed, the word length of the digital processor is determined by system considerations other than I/O requirements, which word length determines the width of the I/O data bus. Typically computer word lengths are integral multiples of 8 whereby a 16 bit word length may typically be utilized. Commercially procurable analog-to-digital and digital-to-analog converters typically provide approximately 12 bits of resolution and therefore in prior art systems when the 12 bit analog information is being entered or received from the data bus the availability of the additional data bus bits is not efficiently utilized. This also requires the sequential handling of the analog, digital and discrete data thereby requring considerable amounts of computer time to perform the input/output functions.
As discussed above, the prior art systems utilize data entry and mode selection keyboards with numerous selection keys, the outputs of which are encoded with the encoded data being applied to the data bus. This prior art arrangement requires complex circuitry to perform not only the encoding function but also to debounce the keyboard and mode selection switches.